The invention generally relates to Differential Phase Shift Keying (D-PSK) demodulation techniques.
D-PSK modulation is a popular modulation techniques used in modern wireless communication. One conventional D-PSK demodulation arrangement utilizes a differential/correlation technique applied to two adjacent symbols received from a communication channel. This is referred to as a “non-coherent” technique. Such a D-PSK technique is optimal based on the assumption that two adjacent received symbols are subject to a same unknown phase rotation in a propagation channel. However, in an Additive White Gaussian Noise (AWGN) or a static channel or any case where channel estimation is available, the conventional D-PSK technique does not take advantage of known channel information, and thus, does not provide optimal performance. Based on the basic non-coherent/correlation approach, several variations have been proposed by assuming different channel characteristics and exploiting different optimization criterions. Such proposals are described in the following literature: D. Divsalar and M. Simon, “Multiple-symbol differential detection of MPSK,” IEEE Trans. Communication, vol. 38, no. 3, March 1990, pp. 300-308; P. C. Wong and P. T. Mathiopoulos, “Nonredundant error correction analysis and evaluation of differential detected pi/4-shift DQPSK systems in a combined CCI and AWGN environment,” IEEE Trans. Vehicular Technology, vol. 41, no. 1 February 1992, pp. 35-48; T. C. Hewavithana and M. Brookes, “Soft decisions for DQPSK demodulation for the Viterbi decoding of the convolutional codes,” Proceedings of 2003 International Conference on Acoustic, Speech and Signal Processing, pp. IV-17-IV-20.
“Phase-shift keying” (PSK) refers to all modulation formats in which the phase of a carrier is modulated. When the carrier is modulated with two distinct phases the modulation scheme is referred to as “binary PSK”. When the carrier is modulated with four distinct phases the modulation scheme is referred to as “Quadratic PSK” (QPSK). PSK formats are widely used in wireless communication, networking, 802.11, WLAN, RFID, 802.15 Bluetooth, etc. PSK and D-PSK differ in the manner of encoding/decoding on the transmit/receive sides. D-PSK (Differential-PSK) modulation represents information bits by the phase shift of a symbol with respect to a previous symbol rather than with respect to an absolute reference. For D-QPSK, the phase shift between two adjacent symbols represents two bits.
Various D-PSK applications are described in the US patent literature. The following list is merely exemplary:
U.S. Pat. No. 4,035,767—Chin (Jul. 12, 1977);
U.S. Pat. No. 4,696,056—Morita (Sep. 22, 1987);
U.S. Pat. No. 5,193,223—Walczak (Mar. 9, 1993);
U.S. Pat. No. 5,528,631—Hayashi (Jun. 18, 1996);
U.S. Pat. No. 5,202,643—Sato (Apr. 13, 1993);
U.S. Pat. No. 5,363,410—Hayashi (Nov. 8, 1994);
U.S. Pat. No. 5,379,323—Nakaya (Jan. 3, 1995);
U.S. Pat. No. 5,369,378—Iinuma (Nov. 29, 1994);
U.S. Pat. No. 5,550,506—Tsumura (Aug. 27, 1996);
U.S. Pat. No. 5,550,868—Boccuzzi (Aug. 27, 1996);
U.S. Pat. No. 5,814,816—Nadolink (Sep. 29, 1998);
U.S. Pat. No. 5,446,422—Mattila (Aug. 29, 1995);
U.S. Pat. No. 5,369,378—Kosaka (Nov. 29, 1994);
U.S. Pat. No. 5,438,592—Boccuzzi (Aug. 1, 1995);
U.S. Pat. No. 6,097,768—Janesch (Aug. 1, 2000).